The present invention relates to a charged piston internal combustion engine having several parallel-operating exhaust gas turbochargers.
In piston internal combustion engines, exhaust gas turbochargers, for increasing the charge air pressure and the charge air volume, are shut down when the yield of exhaust gas energy is reduced in comparison to the full-load operation. This condition occurs, for example, in the partial-load and partial-speed operation of the piston internal combustion engine. In this case, when there is a low yield of exhaust gas energy, only one exhaust gas turbocharger is operated; however, when the power of the piston internal combustion engine increases, gradually one or several further exhaust gas turbochargers are connected in parallel until finally, during the full-load operation of the engine, all existing exhaust gas turbochargers will be operating.
A piston internal combustion engine of this type is disclosed by German Patent Applicaiton (DE) 34 11 408 C2. When the load of the piston internal combustion engine is low, one exhaust gas turbocharger is disconnected from the exhaust gas collector pipe by an exhaust gas blocking device controlled by the charge air pressure. In this case, a charge air blocking device in the suction pipe of the charge air compressor prevents charge air from flowing out of the charge air collector pipe and into the suction pipe. The momentarily existing charge air pressure builds up all over the compressor part of the disconnected exhaust gas turbocharger from the direction of the charge air collector pipe and leading to the charge air blocking device.
This arrangement has a disadvantage in that the requirement of a rapid and high power increase can be met only insufficiently because the piston internal combustion engine cannot follow rapid variations of a desired load requirement before the connecting operation of a previously disconnected exhaust gas turbochargers is concluded. This connection sequence of disconnected turbochargers is delayed by the fact that the charge air compressor of the disconnected exhaust gas turbocharger needs some time in order to reduce the charge air pressure, which at first still exists in its suction pipe downstream of the charge air blocking device, to the opening pressure of the charge air blocking device.
It is another disadvantage of the above-noted arrangement in that the running parts of the connected exhaust gas turbocharger are first accelerated to an overspeed which is also a result of the delayed pressure reduction in the suction pipe of the pertaining charge air compressor. The reason is that, as long as no pressure difference exists at the charge air compressor between the suction and the pressure side thereof, its power intake is low in comparison to the driving power already available at the assigned exhaust gas turbine. The equilibrium between supplied and taken in power of an exhaust gas turbocharger, at the point in time of the start of the connecting operation, takes place in an area of the characteristic diagram of the exhaust gas turbocharger which has an unacceptably high rotational speed. However, this high rotational speed results in thermal as well as mechanical stress to the running parts of the exhaust gas turbocharger reducing its durability.
The described disadvantages occur in piston internal combustion engines with single-stage as well as with dual-stage charging. The only difference is that, in the case of a single-stage charging, both problems occur at the same exhaust gas turbocharger and, in the case of a dual-stage charging, the switching delay relates to the low-pressure exhaust gas turbocharger and the overspeed problem relates to the high-pressure exhaust gas turbocharger.
It is therefore an object of the present invention to provide an arrangement for a piston internal combustion engine of the above-mentioned type which permits a fast power connecting operation to the nominal output and avoids thermal and/or mechanical overloading of the exhaust gas turbocharger to be connected.
According to the invention, this object and other objects are is achieved by the opening of a bypass blocking device at the point in time of the triggering of the connecting operation which causes an immediate pressure relief in the suction pipe of the connected charge air compressor. The conditions that are required for an optimal operation of the connected exhaust gas turbocharger are therefore obtained very rapidly on the air side at the connected exhaust gas turbocharger.
For a piston internal combustion engine of the above-mentioned type with a dual-stage charging, an advantageous further embodiment of the invention is also provided.
Principal advantages achieved by preferred embodiments of the invention include that interference with the power increase by the switching delay is eliminated when an exhaust gas turbocharger is connected; that the overspeed occurring during the connecting of an exhaust gas turbocharger is avoided; that in dual-stage charging, the acceleration of the connected low-pressure exhaust gas turbocharger is also improved; and that a simple control of the blocking device is obtained which controls the bypass pipe arranged between the suction pipes of the charge air compressor since a monitoring with respect to the closing is absent.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.